Myocardial ischemia followed by reperfusion (MI/R) results in cardiac contractile dysfunction. Reperfusion injury is characterized by: 1) a decrease in the basal release of endothelium-derived nitric oxide (NO) (endothelial dysfunction); 2) enhanced polymorphonuclear leukocyte (PMN)-endothelium interaction; 3) PMN infiltration into the myocardium. Protein kinase C (PKC) inhibition of the post-ischemic coronary endothelium preserves basal endothelial NO release and inhibits the subsequent PMN adherence and transmigration into post-ischemic cardiac tissue. The role of specific PKC isoforms, particularly, PKC beta II and zeta, mediating coronary endothelial dysfunction and PMN activation in MI/R is poorly understood. Isoform specific PKC inhibitors have the potential to be highly selective therapeutic tools in the treatment of clinical MI/R such as coronary angioplasty and in heart transplantation. The current project will test the hypothesis that inhibiting PKC beta II and/or PKC zeta will prove to be cardioprotective in the setting of MI/R. The hypothesis will be tested by these specific aims: 1) Left ventricular developed pressure (LVDP) and the maximal rate of LVDP (+dP/dt max) will be measured in the isolated perfused rat heart in the presence and absence of the PKC beta II peptide inhibitor, a PKC zeta peptide inhibitor, and the combination of PKC beta II and zeta inhibitors. The PKC inhibitors will be diluted in plasma and co-infused with PMNs into the heart during reperfusion; 2) Basal NO release from rat aortic endothelium will be measured in the presence / absence of the PKC beta II inhibitor and/or the PKC zeta inhibitor; 3) Superoxide release from rat PMNs will be measured when stimulated with formyI-Met-Leu-Phe (fMLP) or phorbol-12-myristate-13-acetate (PMA) in the presence / absence of the PKC beta II inhibitor and/or the PKC zeta inhibitor; 4) PMN chemotaxis will be measured when primed with fMLP or PMA in the presence / absence of the PKC beta II inhibitor and/or the PKC zeta inhibitor; 5) PMN coronary vascular adherence, infiltration and endothelial adhesion molecule expression in post-ischemic cardiac tissue will be evaluated in the presence / absence of the PKC inhibitors. It is anticipated that PKC beta II and/or zeta inhibition will significantly improve LVDP, +dP/dt max and endothelial basal NO release, decrease PMN superoxide release, chemotaxis, infiltration and endothelial adhesion molecule expression compared to controls.